a Light-duty truck categories LDT1-LDT4 were not created until 1994.
From 1968 to 1978 all trucks with a GVWR up to 6,000 pounds were classified
as light-duty trucks and were required to meet the same standards. As of 1979,
the maximum weight was raised to 8,500 pounds GVWR. During 1988-93, light-duty
trucks were divided into two subcategories that coincide with the current LDT1-LDT4
categories. The standards for LDT1, LDT2, and LDT3 are given in tables 4-30a,
4-40b, and 4-30c.

b The test procedure for measuring exhaust emissions has changed
several times over the course of vehicle emissions regulation. The 7-mode procedure
was used through model year 1971 and was replaced by the CVS-72 procedure beginning
in model year 1972. The CVS-75 procedure became the test procedure as of model
year 1975. While it may appear that the total HC and CO standards were relaxed
in 1972-74, these standards were actually more stringent due to the more stringent
nature of the CVS-72 test procedure.

Additional standards for CO and composite standards for NMHC and NOx tested
over the new Supplemental Federal Test Procedure will be phased-in beginning
with model year 2002. These standards are not shown in this table.

c Emissions standards had to be met for a full useful life of 5
years/50,000 miles through model year 1983, and a full useful life of 11 years/120,000
miles was defined for 1985-93 (several useful life options were available for
1984). Beginning in model year 1996, emissions standards were established for
an intermediate useful life of 5 years/50,000 miles as well as a full useful
life of 11 years/120,000 miles (intermediate and full useful life standards
are shown in parentheses). This applied to all pollutants except HC and particulates
for all LDT4 vehicles and NOx for diesel-powered LDT4 vehicles, which were only
required to meet full useful life standards. Tier 1 exhaust standards were phased-in
during 1996-97 at a rate of 50% and 100%, respectively.

d The cold CO emissions standard is measured at 20 0F
(rather than 75 0F) and is applicable for a 5-year/50,000-mile useful
life.

eGVWR is the maximum design loaded weight. ALVW is the numerical
average of the GVWR and the curb weight.

f Manufacturers can opt to certify vehicles for a full useful life
of 15 years/150,000 miles and either have (1) intermediate useful life standards
waived or (2) receive additional NOx credits.

g The "Prior to control" column reports emissions estimates
of a typical newly manufactured car in the years before exhaust emissions certification
standards were implemented.

h No estimate available.

i In 1968-69, exhaust emissions standards were issued in parts per
million rather than grams per mile and are, therefore, incompatible with this
table.

j No standard has been set.

k The term "tier" refers to a level of standards for specific
years. Interim 2 refers to an intermediate level of standards that moves manufacturers
toward compliance with Tier 2 standards. Interim Tier 2 and Tier 2 standards
are established as "bins." Each bin is a set of standards for NOx,
CO, NMOG, formaldehyde, and particulate matter (HC and non-methane HC standards
are dropped for Tier 2 and interim Tier 2). Manufacturers may certify any given
vehicle family to any of the bins available for that vehicle class as long as
the resulting sales-weighted corporate average NOx standard is met for full
useful life. The Tier 2 corporate average NOx standard is 0.07 grams/mile. Interim
corporate-based average NOx standards are based on vehicle type. The interim
corporate sales-weighted average for LDT4 vehicles is 0.6 grams/mile. Tier 2
standards will be phased in during 2008 and 2009. In 2008, 50% of LDT4 vehicles
must meet Tier 2 standards; the others must meet Interim Tier 2 standards. Beginning
in 2009, all LDT4 vehicles must meet Tier 2 standards.